FIO-8210: fix nested form validation

[AlexeyNikipelau]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-8210

Description

Fix how filter post processor handles data object model type

Breaking Changes / Backwards Compatibility

no

Dependencies

no

How has this PR been tested?

manually

Checklist:

• I have completed the above PR template
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
• New and existing unit/integration tests pass locally with my changes
• Any dependent changes have corresponding PRs that are listed above

[johnformio]

Where are the tests?